1) a tool, such as a socket wrench
2) (corruption of "wretched"), derogatory hip-hop slang for an unpopular, obese, average-looking, rude, closet poly, hip-hop person, usually a welfare client with children from multiple parents, substance abuse problems and a narcissistic personality disorder, hence the multiple partners and nightclub brawling. Often wears ill-fitting leggings, torn fishnet hose and a loose, matted hair weave in a bright color. Extra income may come from multiple partners, begging and/or prostitution, due to hir poverty. Term is often hypocritically used by similar speakers. Warning! This term is a racial stereotype, sexist fat and slut-shaming speech and may provoke ethnic violence from target.
3) hip-hop slang for gun, knife, or assaulting someone. See meanings 1 and 2.
4) Science fiction video game character from "Ratchet & Clank" series
5) Science fiction robot character from "Transformers" animated series.

1) "Hand me the ratchet from my toolbox," said my father as he worked on his car.
2) "That person is soooo ratchet, in that bad weave and tore-up stockings!"
3) "Let's ratchet that mutha#@%$," he said and pulled a 9-mm. ratchet on him.

The Urban Dictionary T-Shirt

A term that Ignorant people use to describe others.
People of this sort are calling each other a type of wrench, that moves in a ratcheting motion, It is not a name to call someone, it is a tool often used to work on things with nuts and bolts!

The mechanic used the ratchet to remove the oil drain plug from the automobile.

The Urban Dictionary T-Shirt

A type of lockback folding knife originally from Germany. These are very popular in much of the Africa and much of the Caribbean. Ratchet Knives are often associated with gangs and criminal activity. In Jamaica they were closely linked with "Rude Boy" street culture.
Ratchet Knives are named for the ratcheted blade lock mechanism.

The ratcheted blade lock mechanism keeps the blade from snapping shut on the user's hand even when only partially opened. The ratchet knife is usually unlocked by using a pull ring on the back rather than the more common push buttons or levers of most lock blades.
Both of these features make it less likely for the knife to snap shut across the user's fingers during a struggle.

However the key to the popularity of these knives is mostly due to their extremely low price, wide availability and intimidating ratchet sound on opening.
The most famous brand of ratchet knife is the Okapi. Originally made in Germany for export to German territories in Africa the production of Okapi knives moved to South Africa during the 1980's where it is still a very popular all around knife, especially with local criminals.
The Okapi was also the favored ratchet of Jamaican rude boys who often referred to them as "Three Star Ratchets" due to the three stars inlaid on the handles of many Okapi brand ratchet knives.